JPWO2018181011A1 - Biaxially oriented polypropylene resin film - Google Patents

Abstract

To provide a polypropylene-based resin film having sufficient heat sealing strength and sealing property for packaging heavy objects and suitable for automatic packaging processing. The melting point of the resin constituting the base layer (A) and the seal layer (C) of the biaxially oriented polypropylene resin film composed of the base layer (A), the intermediate layer (B) and the seal layer (C) is specified. A biaxially oriented polypropylene-based resin film having a specific range in which the ratio of each thickness of the intermediate layer (B) and the seal layer (C) to the total thickness is in a specific range.

Description

  The present invention relates to a biaxially oriented polypropylene-based resin film, and more particularly, to a biaxially oriented film having heat seal strength and sealing properties sufficient for packaging heavy objects, and which can be suitably used for automatic filling and packaging. The present invention relates to a polypropylene resin film.

Conventionally, as a heat-sealable film used for packaging, a non-stretched polyethylene resin film or a laminated polypropylene resin film obtained by laminating an unstretched polypropylene resin film and a stretched polypropylene resin film, or a high melting point polypropylene film Laminated polypropylene resin films obtained by laminating coextruding a low-melting polyolefin-based resin layer onto a resin layer and stretching the same are widely used.
However, a laminated polypropylene resin film obtained by laminating an unoriented polyethylene resin film or an unoriented polypropylene resin film and an oriented polypropylene resin film has a sufficient sealing strength, but requires a lamination step using an organic solvent or the like. However, it is not preferable from the viewpoint of economical effects on the global environment.
In addition, a laminated polypropylene resin film obtained by laminating and co-extruding a low-melting polyolefin resin layer on a high-melting polypropylene resin layer and stretching it has a certain degree of sealing strength, but it is difficult to remove heavy objects such as water. There was no seal strength before packaging.

By laminating an intermediate layer between a base layer made of polypropylene resin and a seal layer made of low-melting polyolefin resin, heat seal strength and sealing properties are improved, and even when heavy items are packaged, the seal part is It is disclosed that the adhesive does not peel off and the contents do not leak from the seal (for example, see Patent Document 1).
However, this film is subjected to a bag-making process in which the contents are wrapped and then heat-sealed continuously, that is, the bag-making product obtained by the so-called automatic packaging process is wrinkled, or the film is formed during the automatic packaging process. There is a problem that it is not transported smoothly.

Japanese Patent No. 4894340

  The present invention solves the above-mentioned problems of the conventional laminated polypropylene film, has a sufficient heat sealing strength and sealing property for packaging heavy objects, can smoothly perform automatic packaging processing, and obtains the obtained product. An object of the present invention is to provide a biaxially oriented polypropylene-based resin film which has less wrinkles and less air return to a vacuum-degassed bag product in addition to less wrinkles.

  The present inventors have conducted intensive studies in order to achieve such an object, and as a result, have found that a biaxially oriented polypropylene-based resin film composed of a base layer (A), an intermediate layer (B) and a seal layer (C) has a base layer ( A) The melting point of the resin constituting the sealing layer (C) is set to a specific range, and the ratio of the thickness of each of the intermediate layer (B) and the sealing layer (C) to the total thickness and the total thickness of the film are specified. By setting it within the range, it has sufficient sealing strength and sealing property to pack heavy objects, can smoothly transport the film in automatic packaging processing, and it is difficult for the obtained bag-made product to wrinkle In addition, the inventors have found that there is little air return to the vacuum-degassed bag-made product, and have reached the present invention.

That is, the present invention
1. A biaxially oriented polypropylene-based resin film comprising a base layer (A), an intermediate layer (B) and a seal layer (C), characterized by satisfying the following 1) to 5): the film.
1) The resin composition constituting the base material layer (A) is mainly composed of a polypropylene resin and has a melting point of 156 ° C. or more.
2) at least the resin composition constituting the intermediate layer (B) is selected from the group consisting of propylene / ethylene / butene-1 copolymer, propylene / butene-1 copolymer, and propylene / ethylene copolymer One type of copolymer is contained in an amount of 30% by weight or more.
3) at least one resin selected from the group consisting of a propylene / butene-1 copolymer, a propylene / ethylene / butene-1 copolymer, and a propylene / ethylene copolymer, wherein the resin composition constituting the seal layer (C) is It is mainly composed of a kind of copolymer and has a melting point of 135 ° C. or less.
4) The thickness of the seal layer (C) is 2% or more and 8% or less with respect to all layers of the film.
5) The thickness of the intermediate layer (B) is 5% or more and 18% or less based on all layers of the film.
6) The sum of the thickness of the seal layer (C) and the thickness of the intermediate layer (B) is not more than 22% with respect to all the layers of the film.
7) The thickness of all layers of the film is 33 μm or less.

2. Item 2. The polypropylene resin film according to Item 1, wherein the seal layer (C) contains an antifogging agent.

  According to the present invention, it has sufficient sealing strength and sealing property for packaging heavy objects, can perform automatic packaging smoothly, has less wrinkles in the obtained bag-formed product, and has a vacuum degassed bag-making. It is possible to provide a biaxially oriented polypropylene-based resin film with less air return to the product.

It is a schematic diagram of the shape of the bag created in the Example, and the test piece for heat seal strength measurement. It is a schematic diagram of the sealing evaluation method.

Detailed description of the invention

Hereinafter, embodiments of the biaxially oriented polypropylene resin film of the present invention will be described.
(Base material layer (A))
The resin composition used for the base material layer (A) is mainly composed of a polypropylene resin. As used herein, the polypropylene resin is selected from the group consisting of an isotactic propylene homopolymer insoluble in n-heptane and a copolymer of propylene containing at least 70 mol% of propylene and another α-olefin. It is preferable that it is made of at least one kind of resin.
Such a polypropylene resin is preferably contained in an amount of at least 80% by weight, more preferably at least 90% by weight, based on the resin composition constituting the base material layer (A).
The melting point of the polypropylene resin used for the base material layer (A) needs to be 156 ° C. or higher. The melting point is measured by the method described in Examples described later. If the melting point is less than 156 ° C., the film cannot be transported more smoothly in the automatic packaging process, and wrinkles are more likely to be formed in the obtained bag-formed product.
The term "n-heptane-insoluble" indicates the crystallinity of polypropylene and indicates the safety when used for food packaging, and in the present invention, n-heptane-insoluble according to the Ministry of Health and Welfare Notification No. 20 of February 1982 It is a preferred embodiment to use a material that conforms to (the elution content at the time of extraction at 25 ° C. for 60 minutes is 150 ppm or less [30 ppm or less when the use temperature exceeds 100 ° C.]).

As the α-olefin copolymer component of the copolymer of propylene and another α-olefin, α-olefins having 2 to 8 carbon atoms, for example, ethylene, butene-1, pentene-1, hexene-1, 4, -Methyl-1-pentene and the like are preferred. Here, the copolymer is preferably a random or block copolymer obtained by polymerizing one or two or more α-olefins exemplified above on propylene.
When propylene homopolymerization and a copolymer of propylene containing 70 mol% or more of propylene and another α-olefin are used as a mixture, the total amount of the resin composition used for the base material layer (A) is It is preferable that the content of the copolymer of propylene containing 70% by mole or more of propylene and another α-olefin be 20% by weight or less. It is more preferably at most 10% by weight.

(Intermediate layer (B))
The resin composition constituting the intermediate layer (B) is at least one selected from the group consisting of propylene / ethylene / butene-1 copolymer, propylene / butene-1 copolymer, and propylene / ethylene copolymer. It is necessary to contain the copolymer in an amount of 30% by weight or more. Thereby, the seal reaching strength and the sealability can be improved. It is preferably at least 65% by weight, more preferably at least 80% by weight, particularly preferably at least 90% by weight.
More preferred forms of the propylene-butene-1 copolymer, the propylene-ethylene-butene-1 copolymer, and the propylene-ethylene copolymer are described in the following 1) to 3).

1) Propylene-ethylene-butene-1 copolymer The propylene-ethylene-butene-1 copolymer preferably has a butene content of 5% by weight or more. When the butene content is 5 mol% or more, the adhesion between the sealing layer (C) and the interlayer is improved, and the heat sealing strength and the sealing property are easily improved.
The upper limit of the butene content is not particularly limited, but if the butene content is too large, crystallization is excessively suppressed, and the crystallinity is lower than that of the propylene homopolymer, resulting in lowering the stiffness of the film. .
As the propylene / ethylene / butene-1 copolymer having a high butene content, for example, "FSX66E8" manufactured by Sumitomo Chemical Co., Ltd. can be exemplified.
The propylene / ethylene / butene-1 copolymer is preferably blended in an amount of 65% by weight or more in the resin component constituting the intermediate layer (B). It is more preferably at least 70% by weight, further preferably at most 99% by weight, more preferably at most 95% by weight. By increasing the blending amount of the propylene / ethylene / butene-1 copolymer to 65% by weight or more, the interlayer strength with the sealing layer (C) is increased, so that the heat sealing strength is increased and the sealing property is more easily improved. On the other hand, when the content is 95% by weight or less, the interlayer strength with the base material layer (A) can be increased.

2) Propylene / butene-1 copolymer The butene content in the propylene / butene-1 copolymer is preferably at least 20 mol%. When the butene content is 20 mol% or more, the adhesion between the sealing layer (C) and the interlayer is improved, and the heat sealing strength and the sealing property are improved.
The upper limit of the butene content is not particularly limited, but if the butene content is too large, crystallization is excessively suppressed, and the crystallinity is lower than that of the propylene homopolymer, resulting in lowering the stiffness of the film. .
Examples of the propylene / butene-1 copolymer having a high butene content include "SPX78J1" manufactured by Sumitomo Chemical Co., Ltd. and "XR110H" manufactured by Mitsui Chemicals, Inc.
The propylene / butene-1 copolymer is preferably blended in an amount of 65% by weight or more in the resin component constituting the intermediate layer (B). It is more preferably at least 70% by weight, further preferably at most 99% by weight, more preferably at most 95% by weight. By increasing the blend strength of the propylene / ethylene / butene-1 copolymer to 65% by weight or more, the interlayer strength with the seal layer (C) is increased, so that the heat seal strength can be increased or the sealing property can be easily improved. On the other hand, when the content is 95% by weight or less, the interlayer strength with the base material layer (A) can be increased.

3) Propylene-ethylene copolymer The ethylene content in the propylene-ethylene copolymer is preferably at least 4 mol%. When the ethylene content is 4 mol% or more, the adhesion between the sealing layer (C) and the interlayer is improved, and the heat sealing strength and the sealing property are improved.
The upper limit of the ethylene content is not particularly limited. However, if the ethylene content is too large, crystallization is excessively suppressed, and the crystallinity is lower than that of the propylene homopolymer, which results in lowering the stiffness of the film. .
Examples of the propylene / ethylene copolymer having a high ethylene content include “PC540R” manufactured by Sun Allomer Co., Ltd. and “VM3588FL” manufactured by Mitsui Chemicals, Inc.
The propylene / ethylene copolymer is preferably blended in an amount of 65% by weight or more in the resin component constituting the intermediate layer (B). It is more preferably at least 70% by weight, further preferably at most 99% by weight, more preferably at most 95% by weight. By increasing the blend strength of the propylene / ethylene: butene-1 copolymer to 65% by weight or more, the interlayer strength with the seal layer (C) is increased, so that the heat seal strength can be increased and the sealing property can be easily improved. On the other hand, when the content is 95% by weight or less, the interlayer strength with the base material layer (A) can be increased.

  The propylene copolymer is preferably a propylene-α-olefin copolymer having a cold xylene solubles (CXS) of 3% by weight or less. When a propylene-α-olefin copolymer having a soluble content of cold xylene (CXS) of more than 3% by weight is used, the rigidity tends to be lost, which is not preferable.

The “cold xylene-soluble component” indicates the amount of the amorphous portion contained in the α-olefin copolymer, and “the cold xylene-soluble component is 3% by weight or less” means that It means an α-olefin copolymer having few crystal parts and high crystallinity.
Here, the cold xylene-soluble matter refers to a solution in which 1 g of a sample is completely dissolved in 100 ml of boiling xylene, cooled to 20 ° C., left for 4 hours, and then separated into a precipitate and a solution. It means that the liquid is dried and the weight when dried at 70 ° C. under reduced pressure is measured and the weight% is obtained.
At this time, the cold xylene solubles (CXS) of the entire intermediate layer is preferably 2.5% by weight or less, more preferably 2.4% by weight or less. Further, the content is more preferably not more than 2.2% by weight.

(Seal layer (C))
The resin composition constituting the seal layer (C) is at least one kind selected from the group consisting of a propylene / butene-1 copolymer, a propylene / ethylene / butene-1 copolymer, and a propylene / ethylene copolymer. The copolymer is mainly used, and the melting point of the copolymer needs to be 135 ° C. or less. The melting point is measured by the method described in Examples described later. If the melting point exceeds 135 ° C., heat sealing and improvement in heat sealing strength cannot be expected.
More preferable forms of the propylene / butene-1 copolymer, the propylene / ethylene / butene-1 copolymer, and the propylene / ethylene copolymer are described in the following 1) to 3).

1) The butene content in the propylene / butene-1 copolymer is preferably at least 20 mol%. By setting the content to 20 mol% or more, it is easy to increase the heat sealing strength and to enhance the sealing property.
The upper limit of the butene content is not particularly limited. However, if the butene content is too large, the film surface may be sticky and the slipperiness and the blocking resistance may be reduced. Examples of the propylene / butene-1 copolymer having a high butene content include "SPX78J1" manufactured by Sumitomo Chemical Co., Ltd. and "XR110H" manufactured by Mitsui Chemicals, Inc.
The propylene / butene-1 copolymer is preferably blended in an amount of 65% by weight or more in the resin component constituting the seal layer (C). More preferably, it is 70% by weight or more. , 99% by weight or less, more preferably 95% by weight or less. When the blending ratio of the propylene / butene copolymer is 65% by weight or more, the heat sealing strength can be increased and the sealing property can be easily enhanced. On the other hand, when the content is 95% by weight or less, the interlayer strength with the intermediate layer (B) can be increased.

2) Propylene-ethylene-butene-1 copolymer The propylene-ethylene-butene-1 copolymer preferably has a butene content of 5 mol% or more. The upper limit of the butene content is not particularly limited, but if the butene content is too large, the film surface may be sticky, and slipperiness and blocking resistance may be reduced. Good. As the propylene / ethylene / butene-1 copolymer having a high butene content, for example, "FSX66E8" manufactured by Sumitomo Chemical Co., Ltd. can be exemplified.

3) Propylene-ethylene copolymer The propylene-ethylene copolymer preferably has an ethylene content of 4 mol% or more. The upper limit of the ethylene content is not particularly limited, but if the ethylene content is too large, the film surface may be sticky, and the slipperiness and the blocking resistance may be reduced. Good. Examples of the propylene / ethylene copolymer having a high ethylene content include “PC540R” manufactured by Sun Allomer Co., Ltd. and “VM3588FL” manufactured by Mitsui Chemicals, Inc.

  The melting point of the polypropylene resin constituting the sealing layer (C) of the present invention must be 135 ° C. or less. The melting point is measured by the method described in Examples described later. If the melting point exceeds 135 ° C., heat sealing and improvement in heat sealing strength cannot be expected.

  In the present invention, in the resin forming each layer, various additives and fillers, for example, an antifogging agent, a heat stabilizer, an antioxidant, a light stabilizer, as long as the properties of each layer are not impaired as necessary. Antistatic agent, lubricant, nucleating agent, flame retardant, pigment, dye, calcium carbonate, barium sulfate, magnesium hydroxide, mica, talc, clay, zinc oxide, magnesium oxide, aluminum oxide, antibacterial agent, antifoggant, natural decomposition An additive that imparts properties can be added. Furthermore, other thermoplastic resins, thermoplastic elastomers, rubbers, hydrocarbon resins, petroleum resins and the like may be blended within a range that does not impair the properties of the film of the present invention.

(Biaxially oriented polypropylene resin film)
The polypropylene resin film of the present invention comprises the above-mentioned base material layer (A), intermediate layer (B) and seal layer (C).

It is necessary that the thickness of the sealing layer (C) is 2% or more and 8% or less based on the whole film layer.
Here, when the thickness of the sealing layer (A) is less than 5%, sufficient heat sealing strength and sealing property cannot be obtained. When the thickness of the sealing layer (A) is more than 8%, the film can be smoothly transported in the automatic packaging process, and the obtained bag-made product is hardly wrinkled. More preferably, it is 2% or more and 5% or less.

It is necessary that the thickness of the intermediate layer (B) is 5% or more and 18% or less with respect to all the layers of the film.
Here, when the thickness of the intermediate layer (B) is less than 5%, the strength attained by sealing and the sealing property cannot be sufficiently obtained. When the thickness of the intermediate layer (B) is 18% or less, the transport of the film in the automatic packaging process can be made smooth, and the obtained bag-made product is hardly wrinkled. More preferably, it is 5% or more and 15% or less.

  It is necessary that the sum of the thickness of the intermediate layer (B) and the thickness of the seal layer (C) is 7% or more and 22% or less with respect to the thickness of the entire film. When the sum of the thickness of the intermediate layer (B) and the thickness of the sealing layer (C) is 7% or more of the total thickness of the film, the return of air to the vacuum degassed bag-making product is reduced. When the sum of the thickness of the intermediate layer (B) and the thickness of the seal layer (C) is 22% or less of the total thickness of the film, the film can be transported more smoothly in the automatic packaging process. Wrinkles are less likely to form in the manufactured bag. Preferably it is 10% or more and 22% or less. It is more preferably at least 10% and at most 20%, particularly preferably at least 15% and at most 18%.

  The thickness of the biaxially oriented polypropylene resin film of the present invention needs to be 15 μm or more and 33 μm or less. In this range, the feeling of waist and the reduction of air return to the vacuum-evacuated bag-making product are balanced. It is more preferably 15 μm or more and 30 μm or less, and particularly preferably 15 μm or more and 28 μm or less.

(Production method)
The biaxially oriented polypropylene resin film of the present invention can be produced by the following film forming method, but is not limited thereto.
For example, using an extruder suitable for the number of laminations, melt-lamination by T-die method or inflation method, etc., then cool by cooling roll method, water cooling method or air cooling method to form a laminated film, sequential biaxial stretching method, simultaneous biaxial Examples of the stretching method include a stretching method and a tubular stretching method.
Here, as an example of conditions for manufacturing by the successive biaxial stretching method, a resin melt-extruded from a T-shaped die is cooled and solidified by a casting machine to produce a raw sheet.
The temperature at the time of melt lamination is preferably set in the range of 240 ° C. to 300 ° C. with reference to the melting point of the raw material resin used for each layer. Further, the temperature of the roll to be cast is preferably set between 15 ° C. and 40 ° C. for the purpose of suppressing crystallization of the resin and improving the transparency.
Next, the raw sheet is heated to a temperature suitable for stretching, and then stretched in the flow direction of the sheet using a speed difference between the stretching rolls. The stretching ratio at this time is stable without stretching unevenness. In view of the above, it is preferable to set the value between 3 times and 6 times. The stretching temperature is preferably set between 100 ° C. and 150 ° C. in consideration of stable production without stretching unevenness.
Next, both ears of the longitudinally stretched sheet are gripped by a tenter clip, and stretched while being sequentially expanded in a direction perpendicular to the flow of the sheet while being heated with hot air to a temperature suitable for stretching. In this case, the transverse stretching ratio is preferably set between 7 times and 10 times in consideration of thickness fluctuation and productivity. The stretching temperature is preferably set between 130 ° C. and 180 ° C. in consideration of stable production without unevenness in stretching.
Finally, it is preferable to perform the heat setting treatment in the range of 150 ° C to 200 ° C.

  The biaxially oriented polypropylene resin film of the present invention can be subjected to a surface treatment in order to improve printability, laminability, and the like. Examples of the surface treatment method include, but are not particularly limited to, corona discharge treatment, plasma treatment, flame treatment, and acid treatment. It is preferable to perform a corona discharge treatment, a plasma treatment, and a flame treatment, which can be continuously processed and can be easily performed before the winding step in the production process of the film.

(Film properties)
(Anti-fog properties)
The polypropylene-based resin film of the present invention preferably has an anti-fogging property rating of 3 or more obtained by a measurement method described below. More preferably, the rank is 2 or more, and further preferably, the rank is 1.

(Heat seal rise temperature)
The biaxially oriented polypropylene-based resin film of the present invention preferably has a heat seal rising temperature of 120 ° C. or lower, which is obtained by a measurement method described later. It is more preferably 115 ° C. or lower.

(Achieved heat seal strength)
The biaxially oriented polypropylene resin film of the present invention preferably has an ultimate heat seal strength of 4.5 N / 15 mm or more obtained by a measurement method described later. It is more preferably at least 5 N / 15 mm, even more preferably at least 6 N / 15 mm ° C.

(Sealing)
The biaxially oriented polypropylene-based resin film of the present invention preferably has a sealability rating of 3 or higher, obtained by a measurement method described below. More preferably, the rank is 2 or more, and further preferably, the rank is 1.

(Feeling of bag making)
The biaxially oriented polypropylene-based resin film of the present invention preferably has a rank 3 or higher evaluation of the firmness of the bag-made product obtained by the measurement method described below. More preferably, the rank is 2 or more, and further preferably, the rank is 1.

(Automatic packaging suitability)
In the biaxially oriented polypropylene resin film of the present invention, it is preferable that the evaluation of the suitability for automatic packaging obtained by the measurement method described below is ○ or Δ.好 ま し く is more preferable.

(Air return after deaeration packaging)
In the biaxially oriented polypropylene resin film of the present invention, the evaluation of air return after vacuum degassing packaging obtained by a measurement method described later is preferably ◎ or ○. ◎ is more preferable.
The return of air is related to the above-mentioned sealing property, and is evaluated as a vacuum packaging suitability at a practical level.

(Application)
The biaxially oriented polypropylene resin film of the present invention not only has sufficient heat seal strength for packaging heavy materials, but also has excellent handling properties and good sealing properties, so that wheat flour, rice, Cereals such as wheat, root vegetables such as potatoes, radish and carrots, various types of pickles such as board and italian varieties, takuan pickles, soy sauce pickles, and Nara pickles, various misos, soup stock and mentsuyu, soy sauce Or packaging materials for various seasonings such as sauces, ketchup and mayonnaise, or packaging materials for collective packaging in which several individual packages such as ramen are packaged together.
Further, since it is excellent in film transportability, it can be suitably used as a packaging material used for automatic packaging of vegetables and the like.

  Hereinafter, specific examples of the present invention will be further described with reference to examples, but the present invention is not limited to the following examples unless departing from the gist thereof. The characteristics in this specification were evaluated by the following methods.

(1) Melting point Tm
According to JIS K 7121, the measurement was performed by a differential scanning calorimeter (DSC).
As a condition adjustment, the temperature was raised from room temperature to 200 ° C. at a rate of 30 ° C./min, kept at 200 ° C. for 5 minutes, lowered at a rate of 10 ° C./min to −100 ° C., and kept at −100 ° C. for 5 minutes. As a curve measurement, the temperature was raised from -100 ° C to 200 ° C at a rate of 10 ° C / min.
In the case where there are a plurality of melting peaks, in the case of the heat seal layer (C), the melting peak having the highest temperature was taken as the melting point. In the case of the substrate layer (A), the melting peak at which the temperature was the minimum was taken as the melting point.

(2) Layer Thickness A sample film was cut into a size of 1 cm × 1 cm, embedded in a UV curable resin, and irradiated with UV for 5 minutes to be solidified. Thereafter, a cross-sectional sample was prepared using a microtome, observed with a differential interference microscope, and the thicknesses of the intermediate layer (B) and the seal layer (C) were measured. The sample was measured at five points, and the average value was calculated.

(3) Anti-fog property 1) 300 cc of 50 ° C. hot water is put into a 500 cc upper opening container.
2) Seal the container opening with the film with the antifogging side of the film facing inside.
3) Leave in a cold room at 5 ° C.
4) With the hot water in the container completely cooled to the ambient temperature, the state of dew adhesion on the film surface was evaluated on a five-point scale.
Rank 1: No dew on the entire surface (adhesion area 0)
Rank 2: slight dew adhesion (up to 1/4 adhesion area)
Rank 3: About 1/2 dew adhesion (up to 2/4 adhesion area)
Rank 4: Almost dew adhesion (up to 3/4 adhesion area)
Rank 5: Dew adhesion on the entire surface (adhesion area 3/4 or more)

(4) Heat seal rise temperature The heat seal layers of the sample film are stacked face to face, and a heat gradient tester (manufactured by Toyo Seiki Co., Ltd.) is used. The heat seal pressure is 1 kg / cm ² , the time is 1 second, and the temperature is A temperature at which the heat seal strength becomes 1 N / 15 mm when heat-sealed at a temperature higher by 80 ° C. in increments of 5 ° C. The heat seal layer surfaces of a 5 cm × 20 cm film are opposed to each other, and the temperature is set at a pitch of 5 ° C. Heat-sealing simultaneously with 5 heat-seal bars (seal surface 1 cm x 3 cm), cut the center part to a width of 15 mm, attached to the upper and lower chucks of a tensile tester, and pulled at a pulling speed of 200 mm / min. Was measured, and the heat seal strength was calculated (unit: N / 15 mm).
A linear graph was drawn with the horizontal axis representing temperature and the vertical axis representing heat seal strength. The temperature at which the heat seal strength exceeded 2.5 N / 15 mm was taken as the heat seal rise temperature.

(5) Ultimate heat seal strength The heat seal layers of the sample film were placed face to face, and the heat seal pressure was 1 kg / cm ² , the time was 1 second, and the temperature was 1 ° C. using a thermal gradient tester (manufactured by Toyo Seiki Co., Ltd.). Heat seal from 80 ° C to 150 ° C at a temperature of 5 ° C in increments of 5 ° C, cut the central part to a width of 15mm, attached to the upper and lower chucks of a tensile tester, and measured the heat seal strength when pulled at a pulling speed of 200mm / min. Calculated (unit: N / 15 mm).
The numerical value that reached the maximum strength when the upper limit of the sealing temperature was set to 150 ° C. was defined as the ultimate heat seal ultimate strength.

(6) Sealability Red ink (RECORDER manufactured by CHUGAI KASEI CO. LTD) is applied to a portion where the seal portions in the length direction (MD) and the width direction (TD) of the bag created in the same manner as in the heat seal strength measurement method described above overlap each other. INK) was dropped from the bag inside to the outside of the bag to evaluate the degree of detachment.
Rank 1: Ink accumulates inside the bag, does not penetrate into the seal, and does not leak outside the bag. Rank 2: There is some penetration of the ink into the seal, but does not leak out of the bag. Rank 3: Ink penetrates into the seal, but does not leak out of the bag. Rank 4: Penetrates the ink into the seal, and slightly leaks out of the bag. Rank 5: Ink Leak outside the bag.

(7) Waist feeling of bag-made product In a bag made in the same manner as in the above heat seal strength measurement method, a rice confection having a weight of about 4 g and a size of 25 mm × 75 mm was put into a polyethylene film having a thickness of 25 μm and a size of 80 mm × 140 mm. The product was twisted and packaged, and the handleability of the product was evaluated.
Rank 1: The film has a waist, can be packed in a box, can be easily displayed, and can be displayed easily. Rank 2: When holding a bag, it feels a little easier, but the work can be done without any problems. Rank 4: Lack of waist, feeling less than holding in hand, difficult to work Rank 5: Lack of waist, difficult to work

(8) Suitability for Automatic Packaging A pillow package was produced using a horizontal pillow bag making machine (PP500 type manufactured by Kyoei Printing Machinery Co., Ltd.).
conditions:
Fusing blade; cutting edge angle 60 °
Seal temperature: 370 ° C
Number of shots: 120 bags / min The smoothness during film transport and the degree of wrinkling of the bag-made product were evaluated in the following three grades.
○: Good film transportability, no wrinkles in bag-made product △: Poor film transportability, wrinkles in bag-made product ×: Poor film transportability, wrinkles in bag-made product

(9) Return of air after degassing packaging Two glass repellents (1.5 cm in diameter) were enclosed when making a bag in the same manner as in the automatic packaging suitability measurement method described above. Thereafter, air was evacuated from the inside with a syringe, and a tape was attached to the needle hole to make a vacuum state. Twenty-four hours later, the degree of air return was evaluated based on the degree of ease of movement.
A: A vacuum state is maintained, and there is no air return.
：: The vacuum state is maintained, but a slight return of air is confirmed.
Δ: Vacuum is partially maintained, but air return is confirmed.
X: The vacuum state is not maintained.

(Used polypropylene resin)
The polypropylene resin constituting each layer used in the examples is as follows.
[PP-1]: Propylene homopolymer: "FS2011DG3" manufactured by Sumitomo Chemical Co., Ltd., MFR: 2.5 g / 10 min, melting point: 158 ° C
[PP-2]: Propylene-ethylene-butene random copolymer: "FSX66E8" manufactured by Sumitomo Chemical Co., Ltd., ethylene content: 2.5 mol%, butene content: 7 mol%, MFR: 3.1 g / 10 minutes, melting point: 133 ° C
[PP-3]: Propylene-butene-1 copolymer: "SPX78J1" manufactured by Sumitomo Chemical Co., Ltd., butene content: 25 mol%, MFR: 8.5 g / 10 min, melting point: 128 ° C

(Example 1)
The resin composition constituting each layer used in Example 1 is as follows.
(1) 0.16% by weight of glycerin monostearate (Matsumoto Yushi Seiyaku Co., Ltd., TB-123) as an anti-fogging agent was added to the base layer (A) constituent resin composition [PP-1], and polyoxyethylene was used. (2) 0.2% by weight of stearylamine (Matsumoto Yushi Seiyaku Co., Ltd., TB-12) and 0.6% of polyoxyethylene (2) stearylamine monostearate (Matsumoto Yushi Pharmaceutical Co., Ltd., Elex 334) What added by weight% was used as [PP-4], and 100 weight% was used as a base layer (A) constituent resin composition.

(2) 1.5% by weight of organic polymer fine particles (CS30: Sumitomo Chemical Co., Ltd .: 3.5 μm particle size) in the resin composition [PP-2] constituting the intermediate layer (B), and glycerin monostea as an antifogging agent 0.45% by weight of a rate (Matsumoto Yushi Seiyaku Co., Ltd., TB-123) was melt-mixed at a resin temperature of 240 ° C. to form pellets.
This raw material was used as [PP-5] and used as a resin composition for constituting the intermediate layer (B) at 100% by weight.

(3) Sealing layer (C) Constituent resin composition [PP-3], 1.5% by weight of organic polymer fine particles (CS30: Sumitomo Chemical Co., Ltd .: 3.5 μm particle size), glycerin monostea as an antifogging agent A raw material obtained by melting and mixing 0.50% by weight of a rate (Matsumoto Yushi Seiyaku Co., Ltd., TB-123) at a resin temperature of 240 ° C. and pelletizing was designated as [PP-6].
A mixture obtained by mixing [PP-3] with 50% by weight and [PP-6] with 50% by weight was used as a resin composition constituting the seal layer (C).
Using three melt extruders, the base layer (A) constituent resin composition is melt-extruded from the first extruder at a resin temperature of 280 ° C., and the intermediate layer (B) constituent resin composition is formed by the second extruder. Is melt-extruded at a resin temperature of 250 ° C., and the resin composition for forming the sealing layer (C) is melt-extruded at a resin temperature of 250 ° C. from a third extruder, and the surface layer (B) / base In the order of the material layer (A) / the seal layer (C), the thickness ratio in the T-die is such that the base layer (A) / intermediate layer (B) / seal layer (C) = 21/3/1. The laminate was extruded, cooled and solidified by a cooling roll at 30 ° C. to obtain an unstretched sheet. Subsequently, between the metal rolls heated to 130 ° C., the film was stretched 4.5 times in the machine direction by utilizing the peripheral speed difference, further introduced into a tenter stretching machine, and stretched 9.5 times in the transverse direction. . The preheating section temperature of the tenter stretching machine was 168 ° C, and the stretching section temperature was 155 ° C.

Furthermore, in the latter half of the tenter stretching machine, after performing heat fixing at 163 ° C., a corona discharge treatment was performed on the surface of the base material layer (A) by a corona discharge treatment machine manufactured by Kasuga Electric Co., and then a sealing layer ( In the same manner as in C), a corona discharge treatment was performed, and the film was wound by a film winder to obtain a polypropylene resin film. The final film thickness was 25 μm, and the thickness of each layer was base layer (A) / intermediate layer (B) / seal layer (C) = 21/3/1 (μm).
The obtained film satisfies the requirements of the present invention, has sufficient heat seal strength and ultimate strength at low temperature, sealability, suitability for automatic packaging, feeling of stiffness in bag-formed products, air after degassing packaging. The return was compatible. In addition, the antifogging property was at a level that does not cause any problem in the packaging of fruits and vegetables. Table 1 shows the film composition and physical properties.

(Example 2)
A laminated film was obtained in the same manner as in Example 1 except that the constituent resin composition of the intermediate layer (B) was a mixture of [PP-1] 10% by weight and [PP-5] 90% by weight. The obtained laminated film has sufficient heat-sealing strength and ultimate strength at low temperature as in Example 1, and achieves both sealing performance, suitability for automatic packaging, stiffness in bag-made products, and air return after deaerated packaging. It became something to do. In addition, the antifogging property was at a level that does not cause any problem in the packaging of fruits and vegetables. Table 1 shows the film composition and physical properties.

(Example 3)
A laminated film was obtained in the same manner as in Example 1, except that the constituent resin composition of the intermediate layer (B) was a mixture of [PP-1] 50% by weight and [PP-5] 50% by weight. The obtained laminated film has sufficient heat-sealing strength and ultimate strength at low temperature as in Example 1, and achieves both sealing performance, suitability for automatic packaging, stiffness in bag-made products, and air return after deaerated packaging. It became something to do. In addition, the antifogging property was at a level that does not cause any problem in the packaging of fruits and vegetables. Table 1 shows the film composition and physical properties.

(Example 4)
A laminated film was obtained in the same manner as in Example 1, except that the constituent resin composition of the intermediate layer (B) was a mixture of [PP-1] 70% by weight and [PP-5] 30% by weight. Although the obtained laminated film slightly deteriorated in sealing property, it had sufficient heat sealing strength and ultimate strength at low temperature as in Example 1, suitability for automatic packaging, feeling of stiffness in bag-made products, and after deaeration packaging. Of air return. In addition, the antifogging property was at a level that does not cause any problem in the packaging of fruits and vegetables. Table 1 shows the film composition and physical properties.

(Example 5)
A laminated film was obtained in the same manner as in Example 2, except that the thickness of the base layer (A) was 22.5 μm and the thickness of the intermediate layer (B) was 1.5 μm. Although the obtained laminated film slightly deteriorated in sealing property, it had sufficient heat sealing strength and ultimate strength at low temperature as in Example 2, suitability for automatic packaging, feeling of tightness in bag-made products, and after deaeration packaging. Of air return. In addition, the antifogging property was at a level that does not cause any problem in the packaging of fruits and vegetables. Table 1 shows the film composition and physical properties.

(Example 6)
A laminated film was obtained in the same manner as in Example 2, except that the thickness of the base layer (A) was 20.5 μm and the thickness of the intermediate layer (B) was 3.5 μm. Although the obtained laminated film had a slight decrease in the stiffness of the bag-made product, it had sufficient heat seal strength and ultimate strength at low temperatures as in Example 2, and had good sealability, suitability for automatic packaging, The feeling and the return of air after deaerated packaging are compatible. In addition, the antifogging property was at a level that does not cause any problem in the packaging of fruits and vegetables. Table 1 shows the film composition and physical properties.

(Comparative Example 1)
A laminated film was obtained in the same manner as in Example 1 except that the thickness of the base material layer (A) was set to 24 μm and the intermediate layer (B) was not provided. The obtained laminated film was inferior in airtightness and air return after deaerated packaging. Table 2 shows the film composition and physical properties.

(Comparative Example 2)
A laminated film was obtained in the same manner as in Example 1, except that the thickness of the base layer (A) was 22 μm, the thickness of the sealing layer (C) was 3 μm, and the intermediate layer (B) was not provided. The obtained laminated film was inferior in airtightness and air return after deaerated packaging. Table 2 shows the film composition and physical properties.

(Comparative Example 3)
A laminated film was obtained in the same manner as in Example 2, except that the thickness of the base material layer (A) was 15 μm, the thickness of the intermediate layer (B) was 4 μm, and the thickness of the sealing layer (C) was 1 μm. The obtained laminated film was inferior to the stiffness of the bag-made product. Table 2 shows the film composition and physical properties.

(Comparative Example 4)
A laminated film was obtained in the same manner as in Example 2, except that the constituent resin composition of the base material layer (A) was changed to 100% by weight of [PP-5]. The obtained laminated film was inferior to the stiffness of the bag product. Table 2 shows the film composition and physical properties.

(Comparative Example 5)
A laminated film was obtained in the same manner as in Example 1 except that the constituent resin composition of the intermediate layer (B) was changed to 100% by weight of [PP-4]. The obtained laminated film was inferior in sealability, suitability for automatic packaging, and air return after degassing packaging. Table 2 shows the film composition and physical properties.

(Comparative Example 6)
A laminated film was obtained in the same manner as in Example 1, except that the thickness of the base layer (A) was 23 μm, the thickness of the intermediate layer (B) was 1 μm, and the thickness of the sealing layer (C) was 1 μm. The obtained laminated film was inferior in sealability, suitability for automatic packaging, and air return after degassing packaging. Table 2 shows the film composition and physical properties.

(Comparative Example 7)
A laminated film was obtained in the same manner as in Example 1, except that the thickness of the base material layer (A) was 35 μm, the thickness of the intermediate layer (B) was 5 μm, and the thickness of the sealing layer (C) was 2 μm. The obtained laminated film was inferior in hermeticity and air return after deaerated packaging. Table 2 shows the film composition and physical properties.

  The polypropylene-based resin film of the present invention has sufficient sealing strength and sealing property for packaging heavy objects, can smoothly perform automatic packaging processing, and has less wrinkles in the obtained bag-formed product, and has a vacuum removal property. It is possible to provide a biaxially oriented polypropylene-based resin film with little air return to the noticed bag-made product.

Claims (2)

A biaxially oriented polypropylene-based resin film comprising a base layer (A), an intermediate layer (B) and a seal layer (C), characterized by satisfying the following 1) to 5): the film.
1) The resin composition constituting the base material layer (A) is mainly composed of a polypropylene resin and has a melting point of 156 ° C. or more.
2) at least the resin composition constituting the intermediate layer (B) is selected from the group consisting of propylene / ethylene / butene-1 copolymer, propylene / butene-1 copolymer, and propylene / ethylene copolymer One type of copolymer is contained in an amount of 30% by weight or more.
3) at least one resin selected from the group consisting of a propylene / butene-1 copolymer, a propylene / ethylene / butene-1 copolymer, and a propylene / ethylene copolymer, wherein the resin composition constituting the seal layer (C) is It is mainly composed of a kind of copolymer and has a melting point of 135 ° C. or less.
4) The thickness of the seal layer (C) is 2% or more and 8% or less with respect to all layers of the film.
5) The thickness of the intermediate layer (B) is 5% or more and 18% or less based on all layers of the film.
6) The sum of the thickness of the seal layer (C) and the thickness of the intermediate layer (B) is not more than 22% with respect to all the layers of the film.
7) The thickness of all layers of the film is 33 μm or less.   The polypropylene resin film according to claim 1, wherein the seal layer (C) contains an antifogging agent.

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